Download Formation of z~6 Quasars from Hierarchical Galaxy Mergers

Formation of z~6 Quasars
from Hierarchical Galaxy
Mergers
Yuexing Li et al
Presentation by: William Gray
Definitions and Jargon
¥ QUASAR stands for QUASI-stellAR radio source
¥ Extremely bright and active nucleus of a young
galaxy
¥ Z~6 = about 800 million years after Big Bang.
¥ SED - Spectral Energy Distribution
¥ FIR Galaxy - Far InfraRed Galaxy
¥ BH / SMBH - Black Hole/ Super Massive Black
Hole
Properties of Z~6 Quasar
¥ Low space density (~10^-9 MPC^-3)
¥ High luminosities (M1450• < -26 )
¥ Gunn-Peterson absorption troughs in
their spectra (places them at the end of
the epoch of reionization)
¥ Lack of evolution in their SED
compared to low redshift Quasars
SDS J1148+5251
¥ Most distant quasar know. Discovered
by the Sloan Digital Sky Survey.
¥ Z = 6.42. M1450• = -27.8
¥ Lbol = 1014 Lsun
¥ SMBH = (1-5)*10^9 Msun
¥ Near Solar metallicity in Quasar host
Very rare Quasar
¥ Low abundance of such quasars.
¥ Hosted by massive halos (>1013Msun) in rare
density peaks
¥ !CDM cosmology suggests that small objects
form first and merge - Òhierarchical assemblyÓ
¥ Originates in highly overdense regions in the
initial dark matter density distribution.
¥ Quasar and host form from many gas-rich
mergers.
Cosmological Parameters
Wilkinson microwave Anistropy Probe
WMAP1 - ("m = 0.3, "b = 0.04, "! = 0.7, h = 0.7, ns = 1,
#8 = 0.9)
WMAP3 - ("m = 0.236, "b = 0.042, "! = 0.759, h =
0.732, ns = 0.95, #8 = 0.74)
For the purpose of this paper, the simulations used
WMAP1 values because WMAP3 predicts lower halo
masses and longer formation time. Although they do
compare results using WMAP3.
Little Methodology
¥ 1: Perform a coarse dark matter sim of
volume of 1 h-3 Gpc3 to find candidate
halo for quasar.
¥ 2. Largest halo is candidate for
formation of quasar at z= 6.5
¥ 3. ÒZoom-inÓ on candidate region and
simulation is rerun with higher
resolution
Merger Trees
¥ Traces mergers throughout redshift
¥ The most massive progenitors at each
redshift are traced by tags to identify earlier
progenitors
¥ Groups that contribute >10% of the halo mass
at each time step are progenitors
¥ This will give the history of our suspect
quasar
Halo Mass functions from cosmological simulations.
Coarse Run.
Halo Mass functions from cosmological simulations.
Zoom in Run.
Merging history of the largest halo.
Modeling Mergers major factors
¥Major mergers = mass ratio of the merging galaxies
are near unity.
¥Only the major mergers play the most important
role in the formation and evolution of massive
galaxies
¥Gas in a rotationally supported disk loses angular
momentum through gravitational torques excited by
tidal forces in a merger, driving the growth of SMBH.
This is most effective in a major mergers.
Table of Mergers
Black Hole seeds
¥Need to grow a BH up to 109 Msun in less than 800
million years.
¥1. Pair instability PopIII - BH ~102 Msun
¥2. Hot, dense clumps of gas collapse to form ~106 Msun
¥3. ~20 Msun BHs from direct collapse of self-gravitating
gas due to global instabilities.
¥In simulation - it is necessary for galaxy progenitors to
have massive BH seeds (~105 Msun)
Escaping BHs ?
¥ When galaxies merge, the BHÕs may merge
or be ejected by gravitational recoil.
¥ Depends on: Vesc=ý 2|$[r]|) .
Hierarchical Assembly of the Quasar
¥ Progenitors are very compact and gas rich.
¥ Strong gravitational interactions between the
merging galaxies lead to tidal tails, strong
shocks and efficient gas inflow that triggers
large-scale starbursts.
¥ Highly concentrated gas fuels rapid accretion
onto the SMBH
¥ Z ~14-9, merging systems are small (tens of
kiloparsecs). By Z~ 9-7, scale and strength
are much greater.
Part 2
¥ At Z ~6.5, progenitors galaxies coalesce
SMBH accretion and feedback to a climax.
¥ This feedback introduces a powerful wind that
clears the material around the quasar.
¥ The largest SMBH appears as a optically
bright quasar. After this, the quasar feedback
quenches star formation and quasar activity
dies down.
Star formation
¥ As progenitors undergo strong
interactions, stars form rapidly.
¥ Total SFR : 100 to > 104 Msun/year
¥ By Z < 7, SFR decreases gradually due
to depletion of gas supply and strong
feedback
¥ By Z ~ 6.5 SFR: ~ 100 Msun / year
(order of mag lower than J1148+5251)
Metallicities
¥ Rapid star formation
produces an abundant
mass of heavy
elements.
¥ Dips and jumps are
due to new material
mergers.
¥ Metals are widespread
due to outflows.
Some regions are
supersolar
metallicity.
Due to infalling
material triggering
small scale star
formation.
Growth of SMBH
¥ Total BH accretion rate grows steadily
during assembly.
¥ Eddington ratio: Lbol/Ledd (3.3 10^4 (M/M ) *L )
¥ Although each BH may not accrete at
Eddingtion rate, so growth of quasar is
a collective contribution of each BH.
sun
sun
Escaping BHs?
¥ Emission of gravitational waves carries
away linear momentum, could cause
BH to recoil.
¥ If recoil velocity is greater than escape
velocity, BH escape.
¥ But, simulation shows that recoil/kick
velocity is much smaller than escape
velocities
Evolution of total BH and stellar mass.
Quasar Luminosities
¥ Lbol=%rMc2, %r=0.1
¥ If BHs are spinning, L is
increased by a factor of
4.
¥ Host appears as an
ultraluminous infrared
galaxy (ULIRG) Lbol
>1012Lsun
Quasar lifetimes
Feedback from Starburst Driven wind
¥ Same
simulation run,
but at lower
resolution and
wind model.
¥ Effect of wind
on quasar
evolution is
minor
Number of such Quasars
¥ Depends on
cosmological
constants used.
¥ WMAP1 ~ 36
¥ WMAP3 ~
handful
¥ WMAP3 will
produce fewer
luminous quasars
Era of Reionization
¥ WMAP3 results - universe was 50%
ionized at Z ~9.3
Summary
¥ Find target halo by performing a N-body
simulation in large volume.
¥ Largest halo reaches M ~ 5.4x1012 h-1 Gpc3
through 7 major mergers between Z ~14.4
and Z~6.5
¥ Quasar host galaxy build rapidly through gas
rich mergers.
¥ SFR up to 104 Msun /year
¥ Reaching stellar mass of 1012Msun at Z~6.5
¥ BH accretion reaches 20 Msun/year and M =
2*109 Msun
¥ At peak, this is consistent with J1148-5251
Questions????
Comments????
Rude Remarks????